MATLAB Answers

How is the division of two numbers carried out in Matlab?

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PE
PE on 23 Mar 2018
Commented: PE on 23 Mar 2018
The behavior is as expected when both the denominator and the numerator are in 'double' precision. If either of the two are integer, as in the example below, the rounding error yields unexpected division results.
double(475904) / double(512) = 929.5
int32(475904) / int32(512) = 930
int32(475904) / double(512) = 930
double(475904) / int32(512) = 930

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PE
PE on 23 Mar 2018
Thanks. Here are two not so obvious learnings in Matlab- 1) Data operations that involve both integers result in an integer data type. 2) The division of two integers is rounded to nearest integer by default. If at all one would have to do this operation, idivide( int32(475904), int32(512) ) would be used.

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Answers (1)

John D'Errico
John D'Errico on 23 Mar 2018
Edited: John D'Errico on 23 Mar 2018
Think about what the class of the result is. If you don't know how to use the class function to check that, then learn to read the output of the whos command. (In fact, in newer MATLAB releases, just displaying a variable at the command line tells you the class, if it is not a double.)
Then consider if the result is stored in an integer variable, then why would you expect a non-integer result? That is, an int32 cannot represent non-integers. So MATLAB stores only the integer part, essentially rounding to the nearest integer.
double(4) / int32(3)
ans =
int32
1
double(5) / int32(3)
ans =
int32
2

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PE
PE on 23 Mar 2018
Thanks! This wasn't intuitive given the experience of other languages. But it seems it is clearly documented in Matlab Fundamentals. Thanks for the reference link.

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